The present invention relates to a laser diode which is low in threshold current and stabilized in transverse mode, and a process for producing such a laser diode.
Recently, in order to improve recording density of the recording devices such as optical discs, short wavelength laser diodes have been developed as a light source for writing/reading. For example, laser diodes having oscillation wavelength of 630-670 nm have been produced by forming a double heterostructure with (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P. As a typical example of such short wavelength laser diodes, there is known one in which a current blocking layer is formed with GaAs.
However, use of GaAs for forming the current blocking layer causes problems of enlarged threshold current and reduced stability of the transverse mode.
On the other hand, use of a compound with high Al ratio, such as AlAs with small refractive index, for forming the current blocking layer has not yet been realized since it has the difficult problems such as deposition of polycrystals on the mask during selective epitaxial growth.
Also, in case of using a compound of (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P for forming the current blocking layer, with a high Al compositional ratio as compared with the cladding layers, it is impossible to enhance the difference of the refractive index between the current blocking layer and the cladding layers, and there is a problem that the heat resistance of the laser diode is markedly raised.
Thus, the conventional laser diodes were unsatisfactory, in respects of light output and reliability, for use as a light source for information processing devices such as optical discs.
As a result of the present inventors' studies for solving the above-mentioned defects, it has been found that by forming successively a first cladding layer of first conduction type, an active layer and a second cladding layer of second conduction type on a Group III-V compound single-crystal substrate of first conduction type by a vapor-phase epitaxy method; etching the second cladding layer to form a ridge; and forming a current blocking layer at the lateral side of the ridge by vapor-phase epitaxy method, a small amount of HCl being added to a vapor-phase epitaxial gas for during epitaxy of the current blocking layer, a laser diode wherein the difference of refractive index in the transverse direction is sufficiently large and the threshold current is sufficiently small has been obtained. On the basis of the finding, the present invention has been attained.